Lunar Legend Tsukihime is about an ordinary highschooler called Shiki Tono who one day accidentally kills Arcueid, an ancient vampire princess. After he meets her again a few days later perfectly alive, she decides to team up with him to hunt down other vampires. Shiki, who lives in the Tono mansion with his sister Akiha and the housemaids Jade and Amber, after barely surviving an accident 8 years prior, posesses the special power Eyes of Death, which allows him to kill anything by cutting it with a knife.
Together with Arcueid, he fights the evil church member Ciel, who just wants people to accept her big butt. The story really picks up after Akihiko, one of Shiki's classmates, becomes a Dead Apostle Ancestor and builds a harem of zombie waifus and the Conceptual Weapon Nanako to take over the world. Sex happens.